of boston



(No Model) 4 J. LEWIS 85 F. A. BROWN.

Card and Magnetic Needle for Mariners Compasses.

No. 238,508. Patented March 8.1881.

NPEI'ERS, PNOTO-LITHOGRAPHER, WASmNGToN, D C

UNITE STATES ATENT rarest JOHN LEWIS AND FREDERICK A. BROWN, 0F BOSTON,ASSIGNORS TO THEMSELVES AND EDWARD CUNNINGHAM, OF MILTON, MASS.

CARD AND MAGNETIC NEEDLE FOR MARINERS COMPASSES.

SPECIFICATION forming part of Letters Patent No. 238,508, dated March 8,1881.

Application filed November 29,1880. (N0 model.) A

To all whom it may concern:

Be it known that we, JOHN LEWIs and FREDERICK AUaUsTUs BROWN, of Boston,of the county of Suffolk and State of Massachusetts, have invented a newand useful Improvement in the Cards and Magnetic Needles for MarinersCompasses; and we do hereby declare the same to be described in thefollowing specification and represented in the accompanying drawing,which denotes an under-side view of a compass-card with our inventionapplied to it.

The first part of ourinvention relates to the magnetic needle of suchcard; and it consists in making it with slots extending longitudinallyin it, between its middle and ends, we having found by experiments thata needle when so made is more sensitive or quicker in action and morereliable than when without such slots.

The second part of our invention is for the purpose of preventing theneedle from being affected by local attractions, or by a mass of ironwhen in its vicinity, and we accomplish this by combining with theneedle and the card or circular plate, to which the needle is attached,a series of U-magnets, or a series of sets of U-magnets, arranged atproper distances apart with theiraxes in lines radiating from the centerof the card, and with the north pole of each of such magnets toward thesouth pole of the needle, all being substantially as shown in theaforesaid drawing, in which- A denotes the magnetic needle; or a, thelongitudinal slots thereof; B, the card or divisional plate, which inthis case is shown as a fiat annulus. D D, 810., are the sets ofauxiliary U-magnets, there being six of such sets in all, which inpractice we have found to be generally sufficient. The number, however,may be increased it necessary, and there may be two or more such magnetsin each set.

We have found that when we have the two magnets or sets which are atright angles to the needle stronger in their magnetic power than each ofthe flanking magnets, not only are the effects of local attractionneutralized, but the card or magnetic needle becomes quicker to operateand more sensitive and accurate. While we do not pretend to explain thecause of such, we have found such results to be attained in practice.

In the drawing two U-magnets are shown to each set, except at the eastand west points of the card, where there are three of such magnets ineach of the sets, the magnets being marked m.

Through tests of a compass-card made in accordance with our invention wehave proved it not affected by local attractions such as it would beordinarily subjected to on land or shipboard.

We are aware that a magnetic needle of a lozenge form having atriangular opening in each oneis not new; also, thatit is not new tohave to a compass-card and its needle a series of bar or plate magnetsarranged radially and at equal or about equal distances apart, andhaving their north poles toward the south pole of the needle, theirsouth poles being toward the north pole of the magnet. There aredistinctive differences between such and our invention, as in carryingout the latter we employ horseshoe or U magnets, with the two poles ofeach at the circumference of the circle of compensating magnets, wherebywe bring all the poles of the magnets, as well as those of the needle,in one circumference; and we not only do that, but have the south poleof each magnet or set of magnets between two north poles of the nextadjacent sets, all of which we have found in practice to be productiveof results unattainable from bar or plate magnets arranged radially on acard and flanking the needle.

We would also remark that a magnetic needle made as is ours-via, of arectangular bar tapered at its poles and having a rectangular slot ineach arm-is preferable to the lozenge needle, as above mentioned, itbeing capable of being magnetized much stronger at its poles.

What we claim is as follows:

1. A magnetic needle tapering at its poles, and rectangular in shapebetween them, and slotted in its body, as set forth.

2. A mariners compass-card having a magnetic needle, and provided withhorseshoe or U magnets arranged on the said card circumferentially, andwith all their poles in or about in the circumference of a circleconcentric with the card, and having the north pole of each needle, andthe magnets of the east and West magnet toward the south pole of themagnetic points stronger in their magnetic power than needle of suchcard. either of the others, or sets thereof, all being 3. A marinerscompass-card having a magessentially as specified.

5 netic needle, and provided with horseshoe or JOHN LEWIS U magnetsarranged on it the said card) circumferentially, and with a1 l theirpoles in or FREDERICK BROWN about in the circumference of a circleconcen- WVitnesses: trio with the card, and having the north pole R. H.EDDY,

10 of each magnet toward the south pole of the E. B. PRATT.

